Tone converter



Patented June 4, 1946 TONE CONVERTER James L. Finch, East Rockaway, N. Y assignor to Radio Corporation of America, a corporation of Delaware Application February 22, 1943, Serial No. 476,787

6 Claims. 1

The present invention relates to a signaling means wherein intelli ence is transmitted according to keyed alternating current energy, and relates, more particularly, to a converter for such systems wherein keyed alternating current of one frequency is utilized to key alternating current of another frequency.

An object of the present invention is to improve the operation of tone signal converters."

A further object of the present invention is the-provision of a signal converter which has a minimum eflect on the shape of the signal operated upon. a

Still another object of the-present invention is the provision of a tone converter in which the amplitude of-the output signals is of substantially a constant weight 'in spite of variations in incoming tonelevel. "Weight" is the measure of length of actual marking intervals with relation to the length of balanced characters, that is, those in which marking and spacing intervals are equal. 1

A further object of the present invention is the provision of a high speed signal converter which is operable without difflcult adjustments on different types of radio transmitters.

In accordance with the principles of the presentinvention alternating current wave ener y. which is keyed according .to signal characteristics to be transmitted, is amplified, then rectified, then limited to a uniform amplitude, any remaining tone frequency components are removed and the resultant pure signal applied to a stable and rapid acting amplifier system which controls a utilization circuit such as a' radio transmitter.

The novel features which, it is believed, are characteristic of the present .nvention are pointed out with particularity in the appended claims. The invention will,-however, be more completely understood by reference to the following detailed description which is accompanied by a drawing wherein transformer i has a primary and a secondary winding, across the primary of which a telegraph modulated tone signal is applied. Across the secondary winding of and, hence, will not be described in anydurther detail. The use of one stage of audio frequency amplification for the received tone signal reduces the input signal requirements to a level which will always be available at a transmitting station in spite of variations in line transmission characteristics.

- I have found that it is undesirable to use more secondary winding of transformer 5 is center tapped and has connected across its outer terminals a full wave rectifier 6, preferably of the my contact type or copper oxide disc type. It-

will benoted that the center tap of ,the secondary winding of transformer 5 is not connected directly to ground but is connected to an adjustable point on resistor 8. Resistor 8 constitutes, with resistors 4 and 1, a potential divider across the source of anode power supply 28.

Thus a variable bias may be applied to the rectifier of such amplitude that audio signals or noise below a certain level are not rectified and does not affect thefollowing portions of the circuit. The output of rectifier 6 is connected to a resistor i3 constitutingthe input circuit of a limiter tube 9. Limiter tube 9 is operated at substantially no bias and at a loweplate potential determined by the position of tap IS on resistor l. The plate potential is so determined that for increases of signal input level above a predetermined value no further corresponding increase in plate current of tube 9 is obtained. Therefore, though transformer l is connected a variable level con- .'ofthe amplifier tube 3 are purely conventional the output level of the rectified signals from rectifier 8 may vary considerably, the signal level in the output circuit of tube 9 is substantially constant. Typical signal input values across resistor l3 may vary between 25 volts for marking intervals to zero volts for spacing intervals. Since the signal appearing inthe output circuit of tube 9 may contain some of the tone signal components from the input, a filter circuit In, including a series inductance II and a pair of shunt capacities i2, is provided in the plate circuit. The filter circuit In is so constituted as to reject the tone components of the signal. Thus thesignal appearing across resistor 20 constituting the input circuit of control tube 15 is substantially a pure square wave varying abruptly b tween the zero potential conditioner spacing to 6. A signal converter including an input circuit last mentioned means including a rejection filter for a. carrier wave'carrying intelligence signals, tuned to the frequency of said carrier and a means for rectifying said carrier to obtain said utilization circuit coupled to the output of said v signals, means for limiting said rectified signals filter, said utilization circuit including a keying t to a predetermined level, and means following 5 tube for modulating a second carrier by said said limiting means for removing carrier composignals. nents from said rectified and limited'signals, said JAMES L. FINCH. 

